Scott’s work is relevant to every product from fresh tree nuts and wheat berries to processed cheese and pharmaceuticals. The microbial growth limits he and his colleagues established apply to dried meats, cheesecake, powdered drink mix, and dog food, but also to non-food products like tree bark, hand lotion, and insulation.
Control water activity, prevent microbial growth
Like all organisms, microorganisms rely on available water in food for growth. They take up water by moving it across the cell membrane. This water movement mechanism depends on a water activity gradient—on water moving from a high water activity environment outside the cell to a lower water activity environment within the cell. When water activity outside the cell becomes low enough, it causes osmotic stress: the cell cannot take up water and becomes dormant. The microorganisms are not eliminated, they just become unable to grow enough to cause infection. Different organisms cope with osmotic stress in different ways. That’s why there are different growth limits for each organism. Some types of molds and yeasts have adapted to withstand very low water activity levels.
Table 1 shows water activity growth limits for many common microorganisms.
Water activity and FDA, FSIS, FSMA
If you measure the water activity of any material, you will know which bacteria, molds, or fungi can grow on and in it. By reducing water activity, you can rule out the growth of certain classes of microbes. At low water activities you can preclude the growth of anything at all. Water activity is not a kill step. It’s a control step, and an integral part of many HACCP plans. These well-established microbial growth limits have been incorporated into FDA, FSIS, and other regulations. Water activity is part of the 2013 Food Code’s definition of potentially hazardous foods, which is referenced by the Food Safety Modernization Act (FSMA).
By reducing water activity in your product, you can rule out the growth of certain classes of microbial growth.
While temperature, pH, and several other factors can influence whether an organism will grow in a food product and the rate at which it will grow, water activity may be the most important factor. Most bacteria, for example, do not grow at a water activity range below 0.91, and most molds cease to grow at water activities below 0.70. Water activity in combination with other hurdles, such as pH, temperature, or modified atmosphere packaging, will limit microbial growth even at water activities higher than 0.91.
In order for microorganisms to grow and survive, they need a source of food and water. Most foods contain plenty of molecules such as starches, proteins, and sugars that can serve as food for microorganisms to grow on. Despite there being enough food, microorganisms will not be able to grow though if there is *insufficient available water.*
Solid food supplements cannot work when the body is in dehydrated state. Without prescription of solid food/drugs/ supplements will the patient drink plain water? Not just few cups, but whether enough free water for the whole body's daily functions and self maintenance.
Table 1. shows water activity growth limits for many common microorganisms.
aW 0.97
Bacteria: Clostridium botulinum E,
Pseudomonas fluorescens.
Typical products: fresh meat, fruits,
vegetables, canned fruit, canned vegetablesaW
| 0.95 | Bacteria: Escherichia coli Clostridium perfringens Salmonella spp. Vibrio cholerae Typical products: low-salt bacon, cooked sausages, nasal spray, eye drops |
aW 0.94
Bacteria: Clostridium botulinum A, B
Vibrio parahaemolyticus
Mold: Stachybotrys atra
aW 0.93
Bacteria: Bacillus cereus
Mold: Rhizopus nigricans
Typical products: some cheeses, cured meat (ham)
bakery goods,
evaporated milk, ral liquid
suspensions, topical lotions
aW 0.92
Bacteria: Listeria monocytogenes
aW 0.91
Bacteria: Bacillus subtilis
aW 0.90
Bacteria: Staphylococcus aureus
(anaerobic)
Mold: Trichothecium roseum
Yeast: Saccharomyces
cerevisiae
aW 0.88
Yeast: Candida
aW 0.87
Bacteria: Staphylococcus aureus
(aerobic)
0.85
Mold: Aspergillus clavatus
Typical products: sweetened condensed milk, aged cheeses (cheddar), fermented sausage (salami), dried meats (jerky), bacon, most fruit juice concentrates, chocolate syrup, fruit cake, fondants, cough syrup, oral analgesic suspensions.
aW 0.84
Mold: Byssochlamys nivea
aW 0.83
Mold: Penicillium expansum
Penicillium islandicumPenicillium viridicatum
Yeast: Deharymoces hansenii
aW 0.82
Mold : Aspergillus fumigatus
Aspergillus parasiticus
Mold : Aspergillus fumigatus
Aspergillus parasiticus
aW 0.81
Mold: Penicillium Penicillium cyclopium
Penicillium patulum
aW 0.80
Yeast: Saccharomyces bailii
aw 0.79
Mold: Penicillium martensii
aw 0.78
Mold: Aspergillus flavus
Typical products: jam, marmalade, marzipan, glace fruits, molasses, dried figs, heavily salted fish
aW 0.77
Mold: Aspergillus niger
Aspergillus ochraceous
aW 0.75
Mold: Aspergillus restrictus
Aspergillus candidus
aW 0.71
Mold: Eurotium chevalieri
aW 0.70
Mold: Eurotium amstelodami
aW 0.62
Yeast: Saccharomyces rouxii
Typical products: dried fruits, corn syrup, licorice, marshmallows, chewing gums, dried pet foods
aW 0.61
Mold :Monascus bisporus
aW 0.60
Bacterial: No microbial proliferation
aW 0.50
Bacteria: No microbial proliferation
Typical products: caramels, toffees, honey, noodles, topical ointments
aW 0.40
Bacteria: No microbial proliferation
Typical products: whole egg powder, cocoa, liquid center cough drop
aW 0.30
Typical products: crackers, starch-based snack foods, cake mixes, vitamin tablets, suppositories
aW 0.20
Bacteria: No microbial proliferation
Typical products: boiled sweets, milk powder, infant formula
Showing 1 to 28 of 28 entries
Table 1 (see above). Water activity growth limits for many common microorganisms
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